Carbon cycling in soil has attracted many attentions because of the increasing focus on global warming. Plant residue decomposition in soil is of great importance because of its direct and indirect effects on nutrient bio-availability. Carbon mineralization in soil provides the required carbon dioxide for photosynthesis. On the other hand, excessive amounts of CO2 would contribute to enhancement of global temperature. The objectives of this study were to 1- investigate the effects of plant residues quality on carbon and nitrogen mineralization rates and 2- evaluate non limiting nitrogen condition in soil on carbon mineralization kinetic. Soil samples were collected from 0-15 cm depth, at Chahartagh closed rangeland, Chaharmahal va bakhteiari. Eight predominant range plant including Melilotus officinalis (L.) Lam., Astragalus gossypinus Fischer, Astragalus adscendens Boiss. Haussak, Medicago sativa L., Hordeum bulbosum L., Bromus tomentellus Boiss., Poa pratensis L., Agropyron trichophorum (Link) K. Richt were sampled. To determine carbon mineralization kinetics and net nitrogen mineralization/ immobilization, soil samples were incorporated with plant residues at a rate of 10 g residue-C kg-1 soil and incubating at 50% water holding capacity and 25°C for 45 and 90 days, respectively. Results indicated that on a general basis, leguminous plants possessed greater concentrations on N and lower values of C/N and Lig/N, compared to those of non-legume plants. All results of CO2-C evolution from plant residue-treated soils conformed well to a first-order kinetics equation. The total amount of CO2-C (Cm) evolved from plant residue-treated soils ranged from 2166.8 mg C kg-1 soil for bulbous barley, to 3057.5 mg C kg -1 for alfalfa. The values of C m were highly correlated (r = -0.958, n = 8, P 0/001) with C:N ratio. Net nitrogen mineralization occurred in all treatment and ranged between 3.5 mg N kg -1 soil for bulbous barley, to 342.4 mg N kg -1 for alfalfa. N mineralization was highly correlated (r = -0.993, n = 8, P 0/001) with C/N. The critical value for net N mineralization was 42.8 so that greater values of C/N can be expected to cause net N immobilization. We observed that N supply as ammonium nitrate increased the fraction of cellulose in the plant residues. The correlation between short-term C mineralization and net N mineralization seemed to be time dependen. and the maximum value of the correlation coefficient was observed after 2 days.